Piston safety stop and reversing means for free piston engines



Jan. 13, 1948. F. M. LEWIS 77 PISTON SAFETY STOP AND REVERSING MEANS FOR FREE PISTON ENGINES Filed Aug. 17, 1944 i i v f i :1 T a Q i l Z o I ll m w H 1 1! M a, :J .i

lgtl l Qu' .L. r' j H -l L I mu "I Ir -D- FQANKMLEWIS Patented .lan. 13, 1948 PISTON SAFETY STOP AND REVERSHNG MEANS FOR FREE PISTON ENGINES Frank M. Lewis, Weston, Mass, assignor, by

mesne assignments, to Lima-Hamilton Corporation, New York, N

Virginia 18., a corporation of Application August 1'2, 1944, Serial No. 549,909

4 Claims. (Cl. 123-46) This invention relates to internal combustion engines of the free piston type, and particularly to improvements in the piston cushioning and reversing means.

In the use of such engines, the termination of the working strokes of the pistons is accomplished through the balance of forces acting upon the pistons. Through failure ofcertaln valves or other parts to function properly, it is possible to lose these balancing forces, and should this occur the entire kinetic energy of the piston members on the termination of their outstrokes is directed against the cylinder heads of the compression and bounce chambers in the form of direct metal to metal contact, resulting in structural failures of the engine frame and possibly other parts.

Attempts have been made to guard against this type of failure by incorporation of a direct bounce cylinder which, by compression of air, absorbs the kinetic energy of the'pistons. However, as this entire energy is transformed to compressing the charges in the direct bounce cylinders, extreme pressures and temperatures result which tend to cause a rapid and erratic acceleration of the piston masses on the return or compression strokes as well as considerable thermal losses. Such practice is detrimental in the way of structural stresses and lubrication deficiencies as well as tending toward rough operation and lower efficiency.

The object of the present invention is the provision of novel and eflicient means in association with the direct bounce chambers of a free piston engine which will eliminate the above-noted debrimental features, while still retaining theprotective principles of the pneumatic safety cushion at the termination of the working strokes of the pistons.

The invention is fully described in the following specification, and illustrated in the accompanying drawing, which is a more or less diagrammatical view of a free piston engine embodyingone form of the invention, with parts broken away.

The free piston engine, as shown in the drawing, comprises a frame or casing Z forming at its center a combustion chamber 3, at each of its opposite ends an air compressor chamber 4, and at the outer end of each such last chambers a direct bounce chamber 5. Opposed power pistons 6, 6 operate in the combustion chambers 3 and each of these attaches to an air compressor piston i in the respective chamber 4. Each piston l divides its chamber into an air compressor chamber at its outer end and a-reverse bounce chamber at its inner end, and has a piston 8 projecting from its outer side into the respective direct bounce chamber 5. It will be understood that as combustion of a charge occurs in the chamber 3, the pistons of each set are moved outward causing the pistons I to compress air in the outer ends of chambers 4, and the pistons B to compress air in the respective direct bounce chambers 5 to effect a pneumatic cushion in its outer end to stop the outward movements of the pistons and serve, in part at least, to reverse the piston movements and return the pistons to compress the next charge in the combustion chamber. Compressed air from the cylinders e is discharged into a'scavenging receiver 9 having connection with the combustion chamber 3 through a connection 9', so that scavenging air may be supplied to such chamber at the end of the outward strokes of the pistons,

For the purpose of the present invention, there is provided an auxiliary chamber ill in connection with each direct bounce chamber 5 through ports I l in its side wall, with such ports positioned to be nearly closed by the associated piston 8 when it has completed its normal outward or working stroke. The piston thus acts on its outward stroke to compress a major portion of the displaced air in the auxiliary chamber l 6. Should the piston move outward a sufficient extent to completely close the ports ll, it acts to compress the balance of the displaced air in the remaining small end space l2 of the chamber 5 to stop the piston rapidly and impart reverse movement thereto before the compressor piston strikes the end wall of the compressor chamber a.

In the present instance, the auxiliary chamber to is provided entirely around the cylinder wall of the direct bounce chamber and the ports H are in considerable number, fairly large in diameter, and distributed quite uniformly around said wall to facilitate rapid flow of air. induced by the piston movement. into and out of the auxiliary chamber. The ports ii are preferably positioned so that they will be partially covered at approximately the same time by the piston on its'outward movement. The volume of the auxiliary chamber it) must of course be such as to cause the desired pressure rise to occur therein at the time the piston is on its outward stroke; however, these pressures should be held to a relatively low value in order to assure the best engine operating characteristic. As energy is released to the piston mass by both the air cushion volume and the compressor clearance volume, chamber I0 is relieved of the full load of the piston return strok During the compressing oi air in each chamber ill, a certain percentage of the energy of the associated pistons 0, I and 8. has been absorbed therein, and it the piston 8 passes the ports ii and enters the area II, the air trapped in such area is unable to escape and serves as a pneumatic cushion of relatively small volume but of high I closed direct bounce chamber, an auxiliary champressure and temperature to stop and reverse the motion oi! the pistons. Due to the small volume of air trapped in the safety space l2, its energy is soon expended in initially forcing the pistons inward on a reverse stroke, but, as the ports Ii are uncovered by the piston 8, the larger volume of air compressed in the auxiliary chamber In starts to release its energy on the piston and continues to maintain considerable pressure thereon for an appreciable percentage of the piston instroke. In this manner, a smooth flowot energy to accomplish the return stroke of each piston set at low initial acceleration is assured and a considerable reduction of the energy losses through heat dissipation is obtained.

I wish it understood that my invention is not limited to any specific construction, arrangement or form of the parts, as it is capable of numerous modifications and changes without departing from the spirit of the claims.

Having thus described my invention, what I claim as new, and desire to secure by United states Letters Patent, is:

1. In an internal combustion engine or the free piston type wherein a piston operates in a closed direct bounce chamber, means iorming'an auxiliary chamber in side communication with said bounce chamber in spaced relation to its outer end, whereby a charge of compressed air is stored in the auxiliary chamber during a predetermined portion of the compression movement of the piston short of a possible limit of such movement and is released to the chamber to impart a reverse movement to the piston, and means forming a closed safety space insaid bounce chamber after communication with said auxiliary chamber is cut oil.

2. In an internal combustion engine or the free piston type wherein a piston operates in a her in side communication with said first chamber'in spaced relation 0! its outer end, whereby during the normal outstroke o! the piston an air charge is compressed thereby in the auxiliary chamber and during an abnormal portion of such outstroke an air cushion is compressed in the closed outer end of the bounce chamber, the air cushion acting to stop the outward piston movement.

3. In an internal combustion engine of the tree piston type wherein a piston operates in a direct bounce chamber, means forming an;air storage chamber having one or more ports in communication with the bounce chamber through a side wall thereof and spaced from its outer end to provide a limited closed air cushion safety space in such end, whereby during the normal outstroke of the piston an air charge is compressed thereby in said storage chamber, while on an abnormally long outstroke said port communication is closed by the piston and air is compressed in said closed air cushion safety space with the cushion air acting to stop the outward piston movement short of striking the end wall of the direct bounce chamber.

4. An arrangement as called for in claim 3 in which the air storage chamber formed by said means extends around the bounce chamber and communicates therewith through ports arranged in annular series around the chamber through its wall.

FRANK M. LEWIS.

REFERENCES crran The following references are of record in the file of this patent:

UNITED STATES PATENTS 

